Spread communication system and mobile station thereof

ABSTRACT

A search circuit in a CDMA system which has a plurality of base stations respectively employing different carrier frequencies, the search circuit selects one carrier frequency among the different carrier frequencies to perform a cell search of the one carrier frequency. The search circuit includes a first search unit searching a plurality of carrier frequencies of the DS-CDMA system; and a controller selecting a highest strength or highest correlation value carrier frequency among the plurality of carrier frequencies based on a result of the first search unit, setting the selected carrier frequency as the one carrier frequency among the different carrier frequencies to perform the cell search of the one carrier frequency. A mobile station adopting the search circuit includes a three-stage cell search process.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a DS-CDMA (Direct Sequence-CodeDivision Multiple Access) base station asynchronous cellular system, andmore particularly to an initial cell search method for a mobile stationand a transmission power control method for a perch channel at a basestation, which is combined with the initial cell search method.

2. Description of the Related Art

In recent years, the downsizing and the popularization of a cellularphone, etc. have been rapidly advancing with the size-reduction of aprocessor, etc. In a system accommodating such a cellular phone, acontinuously moving mobile station must be accommodated in a suitablebase station. At the same time, a system which accommodates mobilestations as many as possible is desired for the upcoming popularizationof a cellular phone. However, since an available frequency bandwidth islimited with a conventional frequency division multiplexing technique,the number of mobile stations which can be accommodated is limited as amatter of course. Accordingly, close attentions are currently paid to aCDMA communication using a direct sequence. In the CDMA communication, atransmission signal is spread-modulated with a spread code which differsdepending on each channel accommodated by a base station. On a receivingside, the transmission signal is regenerated by despreading thespread-modulated signal with the same code as that used by the basestation. In this case, the reception signal must be multiplied by thedespread code (the same as that used on the transmitting side) atsuitable timing on the mobile station side, that is, the receiving side.Accordingly, to which channel of which base station a mobile station isto be connected is determined in the initial stage of the communication.At the same time, the multiplication timing of a despread code, which isintended to continuously connect the mobile station to that channel mustbe obtained. Namely, an initial cell search must be made.

The initial cell search is an operation for initially determining avisited cell of a mobile station (the visited cell is an area where aparticular base station can accommodate a mobile station when the mobilestation stays within the visited cell) when the mobile station power isturned on. At this time, the mobile station receives a perch channeltransmitted from the base station, and attempts to obtain theinformation broadcast by the channel. The perch channel is a channelwhich helps a mobile station identify the despread code of the signaltransmitted from a base station, or capture the channel transmitted toobtain despreading timing in the initial cell search.

In the system which is assumed by the present invention and will bedescribed later, a perch channel is spread with a short code forsynchronously capturing the perch channel, and a long code foridentifying the channel from the base station. The perch channel isassumed to be further spread with a group short code indicating to whichgroup the long code used for the perch channel belongs among many longcodes so as to facilitate a long code search. Here, all of the shortcode, the group short code, and the long code are spread codes whichrespectively have their use purposes.

Since which long code is used for a certain downstream channel (achannel used for a communication from a base station to a mobilestation) cannot be identified, it must be identified by examining thelong code of a particular (perch) channel. Additionally, also the phaseof the long code (the despreading timing when the long code is used in acommunication) must be identified.

As the conventional initial cell search method of a DS-CDMA system witha control channel, which uses a long code which differs depending oneach cell and a synchronization short code common to all cells, thetechnique disclosed by the Japanese Laid-open Patent Publication No.10-126380 can be cited. With this conventional technique, the initialcell search for a single-frequency carrier wave signal can be made athigh speed. Furthermore, as the technique obtained by further developingthe above described conventional technique, “A High-speed Cell SearchMethod Using a Long Code Mask in DS-CDMA Base Station AsynchronousCellular” recited in the Electronic Information Communication SocietyResearch and Technical Report RCS96-122) exists. The format of the perchchannel signal to which the above described techniques are applied isshown in FIG. 1.

FIG. 1 shows that a perch channel 100 signal is transmitted from theleft to the right of this figure. A long code is intended to identify achannel accommodated by a base station. When a communication is madeusing the channel identified by the long code used by a certain basestation, signals are transmitted and received by spreading anddespreading the signals with this long code in all cases during a call.The perch channel signal is spread with the long code unique to thechannel, and is further spread with a short code for synchronouslycapturing the perch channel 100 signal, which is common to all of basestations. The beginning portion of the long code, which is spread withthe common short code, does not include a long code. The portion whereno long code exists is further spread with a group short code indicatingto which group the used long code belongs among many long code groups inaddition to the common short code.

This initial cell search method is mainly composed of three stages.These stages are summarized below.

[First Stage] A destination base station whose reception power ismaximized is determined by performing a correlational square amplitudeoperation between a reception signal and a short code, and by taking anaverage value of the correlational square amplitude operation. At thesame time, slot synchronization is made. Here, the slot synchronizationis the timing at which a despreading process is performed with the shortcode, the group short code, and the long code. Additionally, thecorrelational square amplitude calculation is an operation forcalculating the correlation values for an I signal and a Q signal of areception signal, and for squaring and adding the correlation values forthe I signal and the Q signal, which are obtained by the above describedcalculation. This operation is equivalent to an operation for squaringthe length of a vector when the correlation value of a signal isrecognized to be the vector on an I-Q plane where the correlation valuesof the I and the Q signal are respectively indicated by the horizontaland the vertical axes. The reason that the average value of thecorrelational square amplitude calculation is taken is to suppress aninfluence of noise included in a correlation value.

[Second Stage] A group short code corresponding to a plurality of longcodes is identified by using the slot synchronization timing establishedin the first stage. Used to identify the group short code is a methodfor calculating the correlation value of a reception signal with thegroup short code, and for determining whether or not the correlationvalue equal to or larger than a predetermined value is obtained. Longcode candidates are limited at this stage.

[Third Stage] The long code synchronization and the long code of theperch channel are determined based on the result of the correlationalsquare amplitude operation between the reception signal and the longcode. The long code determination method is a method for calculating acorrelation value with a reception signal by using both of the long codeand the common short code, and for determining that the long code usedfor the perch channel is obtained when a predetermined or largercorrelation value is obtained. If this process is unsuccessfullyperformed, the process goes back to the first stage and another longcode candidate is used.

For the details of the conventional initial cell search method, pleaserefer to the above described patent publication or technical document.

However, it is impossible to apply this technique to a DS-CDMA cellularsystem using a perch channel of a multiple-carrier-frequencies signal asit is. This is because perch channels exist at a plurality offrequencies, and the operation for receiving all of the frequencies isessential for the initial cell search in such a system. A solution tothis problem is not recited by the conventional technique. If the abovedescribed conventional initial search method is sequentially performedfor the respective carrier frequencies, in the worst case, theoperations at the first through the third stages may be considered to beperformed for all of the frequencies. In this case, at least a cellsearch time multiplied by the number “Nf” (the number of downstreamcarrier frequencies) of carrier frequencies is required compared withthe case of a single carrier frequency.

Additionally, when many mobile stations concentrate on a single cell inthe conventional DS-CDMA system, mobile stations exceeding the capacityof one base station attempt to access the station, which can possiblylead to a fault such as a communication quality degradation orcommunication disability.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a system which canefficiently accommodate subscribers in respective base stations in aspread communication system using a single-carrier frequency or multiplecarrier frequencies.

A mobile station according to the present invention, which is a mobilestation for use in a spread communication system having a particularchannel for establishing synchronization, comprises: a receiving unitfor receiving a spread signal of a particular channel; a measuring unitfor measuring the strength or correlation value of the spread signalreceived by the receiving unit; a comparing unit for comparing thesignal strength or correlation value, which is measured by the measuringunit, with a predetermined threshold value; a storing unit for storingthe information about the particular channel having the signal strengthor correlation value, which is larger than the predetermined thresholdvalue; and a synchronization establishing unit for establishingsynchronization based on the information stored in the storing unit.

A base station according to the present invention, which is a basestation for use in a spread communication system having a particularchannel for establishing synchronization, comprises: at least onetransmitting unit for transmitting a spread signal on the particularchannel over at least one carrier frequency by varying a transmissionpower; a measuring unit for measuring the number of mobile stationsaccommodated in the local station or the transmission qualities of thereception signals from the mobile stations; and a controlling unit forcontrolling the number of mobile stations accommodated in at least onefrequency by variably controlling the transmission power of the spreadsignal on the particular channel, which is accommodated in at least onefrequency.

A system according to the present invention, which is a spreadcommunication system having a particular channel for establishingsynchronization, comprises: a base station having a capability forcontrolling the transmission power level of the spread signal portionfor establishing synchronization on the particular channel; and a mobilestation having a capability for selecting a base station to be accessedaccording to the transmission power level of the received spread signalportion for establishing synchronization on the particular channel.

According to the present invention, even if a communication serviceusing a plurality of frequencies is provided, a mobile station canselect a channel at a suitable frequency, and access a base station in aspread communication system.

Additionally, the base station can control the frequency which themobile station subscribes by variably controlling the transmission powerof a spread signal when transmitting the spread signal on a particularchannel for establishing synchronization, and can suitably allocatemobile stations to a plurality of frequencies. Furthermore, a certainbase station increases the transmission power more than that in adifferent base station, so that a mobile station accessing the differentbase station can be accommodated by the certain base station. As aresult, mobile stations can be suitably distributed and allocated torespective base stations without imposing a heavy load on only one basestation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows one example of the format of a perch channel signal in aconventional CDMA cellular system;

FIG. 2 is a block diagram showing the configuration of a mobile stationaccording to a first preferred embodiment of the present invention;

FIG. 3 shows one example of a rectifying circuit shown in FIG. 1;

FIG. 4 is a block diagram showing the configuration of a mobile stationaccording to a second preferred embodiment of the present invention;

FIG. 5 is a block diagram showing the configuration of a mobile stationaccording to a third preferred embodiment of the present invention;

FIG. 6 exemplifies the configuration of a square amplitude calculatingcircuit;

FIG. 7 exemplifies the format of data stored in a storing circuit 26shown in FIG. 4;

FIG. 8 is a block diagram showing the configuration of a mobile stationaccording to a fourth preferred embodiment of the present invention;

FIG. 9 is a block diagram showing the configuration of a mobile stationaccording to a fifth preferred embodiment of the present invention;

FIG. 10 is a block diagram showing the configuration of the mobilestation according to a sixth preferred embodiment;

FIG. 11 shows a mobile station according to a seventh preferredembodiment of the present invention (No. 1);

FIG. 12 shows the mobile station according to the seventh preferredembodiment of the present invention (No. 2);

FIG. 13 shows the mobile station according to the seventh preferredembodiment (No. 3);

FIG. 14 shows a mobile station according to an eighth preferredembodiment of the present invention;

FIG. 15 shows a base station according to a first preferred embodimentof the present invention;

FIG. 16 shows a base station according to a second preferred embodimentof the present invention;

FIG. 17 shows a base station according to a third preferred embodimentof the present invention; and

FIG. 18 shows a base station according to a fourth preferred embodimentof the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2 is a block diagram showing the configuration of a mobile stationaccording to a first preferred embodiment of the present invention.

In this preferred embodiment, the presence/absence of a carrier wave isinitially determined for all of carrier frequencies. Then, whether ornot an available perch channel exists is determined in each of thecarrier frequencies by measuring the strength of a reception signal ateach of the carrier frequencies, and by comparing the measured strengthwith a predetermined threshold value. If an available perch channel isdetermined to exist only in some of the carrier frequencies at thisstate, the time taken to despread the frequencies where no necessarysignal exists can be saved by making a cell search for those carrierfrequencies.

The signal received by an antenna 7 is input to a receiving circuit 1.The receiving circuit 1 includes a frequency converting circuit and alocal oscillator, which are not shown in this figure. The frequencyconverting circuit converts the cyclic signal output from the localoscillator into the frequency specified by an externally input digitalsignal, so that the locally oscillated signal that the receiving circuit1 requires to receive a signal can be varied. The receiving circuit 1 isintended to convert the signal received by the antenna 7, for example,into a baseband signal, and to output the baseband signal. The signalreceived by the receiving circuit 1 is an analog signal, and is input toa rectifying circuit 2. The rectifying circuit 2 includes a switch. Therectifying circuit 2 turns off the switch in a cyclic time period duringwhich perch channel signals arrive, and turns on the switch at the endof the cyclic time period to emit the electric charge of the inputanalog signals, which is accumulated in an internally arrangedcapacitor. Namely, the analog signals which are received by the antenna7 and output from the receiving circuit 1 are integrated by therectifying circuit 2. The average value of the signals received duringthe perch channel signal cyclic time period can be obtained if theintegrated value output from the rectifying circuit 2 is divided by thetime (the cyclic time period) taken to integrate the signals. However,the integrated value itself is used to simplify the circuitconfiguration here. The integrated value output from the rectifyingcircuit 2 is A/D-converted by an A/D converter 3. The digital signalobtained by the A/D conversion is compared with a predeterminedthreshold value by a comparing circuit 4. The output of the comparingcircuit 4 becomes “1” when a digital signal exceeding the thresholdvalue is obtained. The signal indicating the value “1” is input to astoring circuit 6 as a Write (Write-enable) signal, so that thefrequency data input to the receiving circuit 1 at this time is storedin the storing circuit 6. This frequency data is provided to the storingcircuit 6 as an Nbf-bit signal from a controlling circuit 5.

The controlling circuit 5 stores the frequencies of a plurality of perchchannels beforehand, and specifies the frequency of the perch channel tobe frequency-detected for the receiving circuit 1 with frequencyspecification data. The receiving circuit 1 receives the perch channelsignal having the frequency specified by the controlling circuit 5. Thereceiving circuit 1 converts the signal having the specified frequency,for example, into a baseband signal, and outputs the baseband signal tothe rectifying circuit 2. The rectifying circuit 2 integrates thesignals input from the receiving circuit 1 during the perch channelsignal cyclic time period by turning on/off the internal switch with thesignal (switching signal) instructing the cyclic time period timing. Asdescribed above, the output of the rectifying circuit 2 is A/D-convertedby the A/D converter 3, and is input to the comparing circuit 4 as anNad-bit digital signal in order to be compared with a threshold value.If the numeric value represented by the Nad bits is larger than thethreshold value as a result of the comparison, a Write signal is appliedto the storing circuit 6, so that the Nbf-bit frequency specificationdata input from the controlling circuit 5 is stored.

The controlling circuit 5 applies a Read signal to the storing circuit6, reads the Nbf-bit frequency data candidate from the storing circuit6, sets the read data in the receiving circuit 1, and makes a cellsearch.

All of the outputs of the controlling circuit 5 and the frequencyspecification data may be stored in the storing circuit 6 without makingthe above described comparison with the threshold value. Additionally,the output of the rectifying circuit 2 is compared with the thresholdvalue of an analog voltage by an analog comparator, so that the resultof the comparison may be used as a Write signal to the storing circuit.Furthermore, the output of the A/D converter 3 is compared with athreshold value by a CPU, etc., so that a frequency candidate data maybe selected.

Note that the configuration for making a cell search is not shown inFIG. 2 although the controlling circuit 5 obtains frequency candidatedata for making a cell search. Because a conventional method can be usedas the cell search method and a known technique can be also used as thehardware configuration, a cell search configuration is not particularlyshown. Accordingly, the cell search method and the hardwareconfiguration implementing this method are not particularly referred toin the explanations to be provided about the preferred embodiments.

FIG. 3 shows one example of the rectifying circuit shown in FIG. 2.

This rectifying circuit is implemented by adding a switch 10 to ageneral bridge-type full-wave rectifying circuit 9. The signal inputfrom an input terminal 8 is rectified by a bridge 9 a and a capacitor 9b. Particularly, in this preferred embodiment, the switch 10 is arrangedand turned off during the perch channel signal cyclic time period. Theelectric charge of the rectified signal is accumulating in the capacitor9 b during this time period. The operation for accumulating the electriccharge of a rectified signal in the capacitor 9 b corresponds to theabove described signal integration. The rectifying circuit may beconfigured by using a half-wave rectifying circuit although FIG. 3exemplifies the configuration using the full-wave rectifying circuit.

FIG. 4 is a block diagram showing the configuration of a mobile stationaccording to a second preferred embodiment of the present invention.

In this figure, the same constituent elements as those shown in FIG. 2are denoted by the same reference numerals.

According to this preferred embodiment, if a signal available for aplurality of carrier frequencies is determined to exist, a cell searchis made for the frequency at which the strength of the signal becomes amaximum among the carrier frequencies where the signal exists. After theabove described process at the first stage is terminated, the cellsearch for a single frequency is made in descending order of thestrength of the signal.

Namely, a receiving circuit 1 to which Nbf-bit frequency specificationdata is input from a controlling circuit 1 performs frequency conversionfor the signal having the frequency specified by this input, and outputsthe signal obtained by the conversion to a rectifying circuit 2. Therectifying circuit 2 rectifies the input signal from the receivingcircuit 1 based on the switching signal input from the controllingcircuit 5, and integrates the signal obtained by the rectificationduring a perch channel signal cyclic time period. The result of theintegration is input to an A/D converter 3. After the signal isconverted into a digital signal, it is input as an Nad-bit digitalsignal to a comparing circuit 4 and also to a storing circuit 6. If theintegrated value of the rectifying circuit 2 is larger than a thresholdvalue as a result of the comparison made by the comparing circuit 4, aWrite signal is input from the comparing circuit 4 to the storingcircuit 6. The Nbf-bit frequency specification data output from thecontrolling circuit 5 and the Nad-bit signal value obtained bydigitizing the integrated value of the rectifying circuit 2 arecorresponded and stored in the storing circuit 6.

The controlling circuit 5 shown in FIG. 4 reads the frequency datacorresponding to the maximum integrated value data from the storingcircuit 6, and makes a conventional cell search for a single frequency.In this case, the controlling circuit 5 references the integrated valuedata stored in the storing circuit 6, searches for the maximumintegrated value data, and obtains the frequency specification datastored in correspondence with the maximum integrated value data. Then,the controlling circuit 5 makes the conventional cell search for asingle frequency for the frequency specified by this frequencyspecification data. Additionally, in the configuration shown in FIG. 4,a method for obtaining a predetermined number of pieces of frequencyspecification data from the storing circuit 6 in descending order of anintegrated value, and for individually making the conventional cellsearch for a single frequency for the plurality of frequencyspecification data, may be used other than the method for using themaximum frequency data as a cell search target. By selecting apredetermined number of frequencies in descending order of an integratedvalue as described above, processing time can be significantly reducedcompared with the case where a cell search is made for all of storedfrequencies. Explanation about the conventional cell search method for asingle frequency is omitted here.

FIG. 5 is a block diagram showing the configuration of a mobile stationaccording to a third preferred embodiment of the present invention.

According to this preferred embodiment, after the timing-correlationalsquare amplitude calculation between the output of the receiving circuit21 and a common short code is made, and a cell search is made based onthis data. Here, the timing-correlational square amplitude calculationmeans the acquisition of correlation values obtained by matched filters,and the information about the timing at which a common short code and ademodulation signal are multiplied.

A receiving circuit 21 includes a frequency converting circuit (notshown), and can set a locally oscillated frequency with externally inputdata by using the frequency converting circuit. The receiving circuit 21generates the signal having the corresponding frequency based on thefrequency specification data provided by a controlling unit 27, andconverts the frequency of the signal received by an antenna 20 by usingthis locally oscillated signal. For example, an RF band signal receivedby the antenna 20 is converted into an IF band signal. Then, the signalwhose frequency is converted by the receiving circuit 21 is input to anorthogonal demodulator 22, where the signal is demodulated into an I andQ signals being orthogonal signals. Then, the I and Q signals arerespectively converted into digital signals by A/D converters 23-1 and23-2, and input to matched filters 24-1 and 24-2. The common short codeof the perch channel signal to be cell-searched is input to the matchedfilters 24-1 and 24-2, which respectively calculate and output thecorrelation values between the common short code and the converteddigital I and Q signals. A square amplitude calculating circuit 25 is acircuit which calculates the square of the distance from the coordinateorigin of the complex number value on a complex plane, by recognizingthe correlation values output from the matched filters 24-1 and 24-2 tobe the real and imaginary number parts of a complex number (for example,respectively recognizes the correlation values between the common shortcode and the I signal and between the common short code and the Q signalto be a real and imaginary number parts), and outputs the calculatedvalue. The output of the square amplitude calculating circuit 25 isstored in the storing circuit 26 as a correlational power value alongwith the frequency specification data output from the controlling unit27. The controlling unit 27 reads the stored data from the storingcircuit 26 by providing a Read signal to the storing circuit 26, andselects a frequency and timing candidates from the stored data. Acorrelation value is stored in the storing circuit 26 each time thematched filters 24-1 and 24-2 multiply a common short code at adifferent timing. Therefore, the timing candidate can be determinedbased on a memory location in the storing circuit 26 according to thecorrespondence between frequency and timing.

FIG. 6 exemplifies the configuration of the square amplitude calculatingcircuit 25.

When the correlation values are obtained respectively for the I and Qsignals which are orthogonally demodulated by the orthogonal demodulator22, the correlation values are respectively input to multipliers 28-1and 28-2 as inputs 1 and 2. The inputs 1 and 2 are branched andrespectively input to the multipliers 28-1 and 28-2. Then, the inputs 1and 2 are respectively squared by the multipliers 28-1 and 28-2, andinput to an adder 29, which adds these values. As a result, acorrelation power value I²+Q² is output from the adder 29 based on theassumption that the values of the inputs 1 and 2 are respectivelyrepresented as I and Q.

FIG. 7 exemplifies the storage format of the data stored in the storingcircuit 26 shown in FIG. 5.

In the storing circuit 26 shown in FIG. 5, data items such as acorrelational power value, a timing candidate, and a frequency candidateare stored. The format shown in FIG. 7 exists as the storage format forefficiently storing these data items from an access or capacityviewpoint. In this figure, a correlational power value is stored in eachcell 71 in a two-dimensional table 70. Each column in the table 70corresponds to each specification frequency “f”, while each row in thetable 70 corresponds to each timing candidate “t”. The timing candidate“t” is the timing at which a common short code is multiplied by ademodulation signal. Normally, when a spread code is provided, a matchedfilter sequentially outputs a correlation value while shifting themultiplication timing of a spread code in synchronization with the clockof a receiving device. Accordingly, the multiplication timing of aspread code, that is, a timing candidate, can be identified at thetiming of the clock within a receiving device by storing in which ordera correlation value is output.

Therefore, a correlational power value is stored in the cell at theintersection point of the multiplication timing (timing candidate) whenthe correlational power value is obtained and a specification frequency.By arranging the storing circuit 26 as the table 70, only correlationalpower values may be stored therein. Furthermore, a column and rowaddresses respectively become frequency specification data (a frequencycandidate) and multiplication timing (a timing candidate) when acorrelation power value is written/read to/from the storing circuit 26.

FIG. 8 is a block diagram showing the configuration of a mobile stationaccording to a fourth preferred embodiment of the present invention.

In this figure, the same constituent elements as those shown in FIG. 5are denoted by the same reference numerals.

The signal received by an antenna 20 is frequency-modulated to an IFband signal by a receiving circuit 21, and is input to an orthogonaldemodulator 22. The orthogonal demodulator 22 demodulates the signalfrom the receiving circuit 21 into an I and Q signals, and respectivelyinputs them to A/D converters 23-1 and 23-2. The I and Q signals whichare converted into digital signals are respectively input to matchedfilters 24-1 and 24-2, which respectively calculate the correlationvalues between the common short code and the I and Q signals. Thecorrelation values of the I and Q signals which are respectively outputfrom the matched filters 24-1 and 24-2 are input to a square amplitudecalculating circuit 25. The square amplitude calculating circuit 25calculates and outputs the total (correlational power value) of thesquares of the correlation values between the common short code and theI and Q signals. The output of the square amplitude calculating circuit25 is input to a storing circuit 26 and also to a comparing circuit 30.The comparing circuit 30 compares the output (correlational power value)of the square amplitude calculating circuit 25 with a predeterminedthreshold value. If the output of the square amplitude calculatingcircuit 25 is larger than the threshold value as a result of thecomparison between the output of the square amplitude calculatingcircuit 25 and the threshold value, the output (determinationinformation) of the comparing circuit 30 becomes “1”. The value “1” isinput to the storing circuit 26 as a Write signal, so that only thefrequency specification data corresponding to the correlational powervalue exceeding the threshold value and the correlation power value arestored in the storing circuit 26.

Then, a controlling unit 27 reads the correlational power value and thefrequency candidate (frequency specification data) corresponding theretofrom the storing circuit 26, selects the timing corresponding to thecorrelational power value (correlational square amplitude calculationvalue), which becomes a maximum at each frequency, and makes aconventional cell search for a single frequency for the frequencycandidate corresponding to this timing. Or, the controlling unit 27 maymake a cell search by selecting the frequency of the maximumcorrelational square amplitude calculation value among all of thefrequencies stored in the storing circuit 26 and its correspondingtiming. The slot timing (the timing at which a common short code and ademodulation signal are multiplied), which corresponds to acorrelational power value, can be known from the relationship betweenthe operations of the matched filters 24-1 and 24-2 and the clock withinthe device by detecting in which order the correlation value is read outamong the correlation values which are sequentially output from thematched filters 24-1 and 24-2.

According to this preferred embodiment, a threshold value determinationis made, and the data about the frequency of a perch channel signal,which is considered to be valid, is stored in the storing circuit 26, sothat the capacity of the storing circuit 26 and the operation amount ofsubsequent data processing (maximum value selection and sorting) can bereduced.

FIG. 9 is a block diagram showing the configuration of a mobile stationaccording to a fifth preferred embodiment of the present invention.

In this figure, the same constituent elements as those shown in FIG. 5are denoted by the same reference numerals.

According to this preferred embodiment, the timing corresponding to thedata of the maximum square amplitude calculation value is determined foreach frequency among the data stored in a storing circuit 26. A maximumvalue determining circuit 31 may be implemented by software with a CPU.Additionally, the maximum value determining circuit 31 may select thetiming corresponding to the maximum square amplitude calculation valueat all of frequencies. Furthermore, the maximum value determiningcircuit 31 may calculate the data stored in the storing circuit 26during a plurality of common short code cyclic time periods, obtain theaveraged data in these cyclic time periods, and determine the maximumvalue among the averaged data.

The signal received by an antenna 20 is frequency-modulated to an IFband signal, and is demodulated by an orthogonal demodulator 22. Afterthe demodulated I and Q signals are respectively converted by A/Dconverters 23-1 and 23-2, the correlation values between a common shortcode and the I and the Q signals are respectively calculated by matchedfilters 24-1 and 24-2. Then, the square amplitude calculation value(correlational power value) of the correlation values of the I and Qsignals is obtained by a square amplitude calculating circuit 25, andthe obtained value is stored in the storing circuit 26. In thispreferred embodiment, a maximum value determining circuit 31 reads thefrequency specification data and the correlational power value, whichare stored in the storing circuit 26, independently from a controllingunit 27, and determines the frequency specification data (frequencycandidate) corresponding to the maximum correlational power value. Asthe way of determining the correlational power value at this time,several methods exist as described above.

When the frequency candidate corresponding to the maximum correlationalpower value is determined by the maximum value determining circuit 31,the controlling unit 27 obtains the frequency candidate and the timingcandidate, which correspond to the maximum correlational power value,from the storing circuit 26 by applying a Read signal to the storingcircuit 26, and makes a cell search.

FIG. 10 is a block diagram showing the configuration of a mobile stationaccording to a sixth preferred embodiment of the present invention.

In this figure, the same constituent elements as those shown in FIG. 9are denoted by the same reference numerals.

According to this preferred embodiment, a cell search is madesequentially from the frequency and the timing, which correspond tolarger correlational square amplitude operation value data, among thetiming-correlational square amplitude calculation value data of all offrequencies.

In this preferred embodiment, the above described cell search capabilitymay be implemented by software with a CPU having a sorting circuit 32which rearranges data such as frequency candidates, timing candidates,etc., which are stored in a storing circuit 26, in descending order of asquare amplitude calculation value. Additionally, data such as thefrequencies, timing data, etc. stored in the storing circuit 26 may berearranged after averaging the data during a plurality of common shortcode cyclic time periods also in this preferred embodiment.

The signal received by an antenna 20 is frequency-modulated to an IFband signal by a receiving circuit 21, and is demodulated by anorthogonal demodulator 22. The demodulated I and Q signals arerespectively converted into digital signals by A/D converters 23-1 and23-2, and the correlation values between a common short code and the Iand Q signals are respectively calculated by matched filters 24-1 and24-2. Then, the correlation values of the I and Q signals are squared bya square amplitude calculating circuit 25, and a correlational powervalue (correlational square amplitude calculation value) of the I and Qsignals is calculated. The obtained value is stored in the storingcircuit 26 along with its corresponding frequency specification data.The sorting circuit 32 searches for the correlational power valuesstored in the storing circuit 26, and rearranges the data within thestoring circuit 26 in descending order of a correlational power values.Or, the sorting circuit 32 first searches the frequency data within thestoring circuit 26, and rearranges the data having the same frequency indescending order of a correlational power value in a group of the datahaving the same frequency.

A controlling unit 27 obtains a frequency and timing candidatessequentially from the data having a larger correlational power valuefrom the storing circuit 26 where the data are rearranged as describedabove, and makes a cell search.

FIGS. 11 through 13 show a mobile station according to a seventhpreferred embodiment of the present invention.

Since signals in a plurality of carrier waves transmitted at the samepower from one base station have almost the same attenuationcharacteristic, no difference is considered to be made whichever signalis adopted. Therefore, only the signal having the maximum correlationalsquare amplitude calculation value is used for a comparison.

FIG. 11 exemplifies the configuration of the mobile station according tothe seventh preferred embodiment.

In this figure, the same constituent elements as those shown in FIG. 10are denoted by the same reference numerals.

The mobile station according to this preferred embodiment comprises acircuit for sorting the data of stored square amplitude calculationvalues, and a circuit for estimatingly classifying the data intorespective base station data.

The sorting and the estimatingly-classifying capabilities areimplemented by software with a CPU 35. However, these capabilities maybe configured by hardware.

The signal received by an antennal 20 is frequency-modulated to an IFband signal, and demodulated into an I and Q signals by an orthogonaldemodulator 22. After the demodulated I and Q signals are respectivelyconverted into digital signals by A/D converters 23-1 and 23-2, they areinput to matched filters 24-1 and 24-2. The correlation values between acommon short code and the digital I and Q signals are calculated by thematched filters 24-1 and 24-2, and the calculation results are output toa square amplitude calculating circuit 25. The square amplitudecalculating circuit 25 respectively calculates the square amplitudes forthe correlation values of the I and Q signals, and calculates thecorrelational power value of the I and Q signals. The calculatedcorrelational power value is transmitted to a CPU 35, which stores thisvalue in a storing circuit 36. At the same time, a process to bedescribed later is performed for this value. Additionally, the CPU 35receives the frequency specification data corresponding to thecorrelational power value stored in the storing circuit 36 from acontrolling unit 27, and stores this data in correspondence with thecorrelational power value.

After the CPU 35 performs a predetermined process, it outputs afrequency and timing candidates to the controlling unit 27 to make thecontrolling unit 27 perform a cell search.

FIG. 12 is a flowchart exemplifying the estimating-classificationprocess executed by the CPU 35 shown in FIG. 11.

In this example, for the data having the same timing, only the datahaving the maximum correlational square amplitude calculation value isleft and the remaining data is discarded. Note that this process may beperformed after stored data is averaged in a plurality of common shortcode cyclic time periods.

FIG. 13 exemplifies the data arrangement in the storing circuit 3.

In the storing circuit 36, records, each of which is composed of dataitems such as a ranking, frequency data, timing (phase), and acorrelational square amplitude calculation value, are stored in the formof a table. Each data item is composed of 1 word, and each record iscomposed of 4 words. Since one-word data is stored at one address in thestoring circuit 36, a read/write operation can be made from/to eachrecord in units of data items.

Here, the storage unit of each record is assumed to be referred to as anentry in the storing circuit 36. Additionally, as shown in FIG. 13, theentry address at which the first record of the storing circuit 36 isstored is assumed to be “DataStart”, while the entry address at whichthe last record is stored is assumed to be “DataEnd”.

In such a configuration, “N” records with the rankings 1 through “N” arestored in the respective entries addressed at “DataStart”,“DataStart+4”, “DataStart+8”, . . . , “DataEnd”.

The estimatingly-classifying process executed by the CPU 35 is explainedby referring to FIGS. 12 and 13. Assume that records are rearranged indescending order of a correlational square amplitude calculation valueas illustrated in FIG. 13 before the process shown by the flowchart ofFIG. 12 is executed. Also this process is performed by the CPU 35. Afterthe process of the flowchart shown in FIG. 12 is performed, desiredrecords are arranged in descending order of a correlational squareamplitude calculation value at addresses “DataStart” to “DataEnd+3”.Also this arrangement process is performed by the CPU 35. As a matter ofcourse, data arranged in ascending order can be generated.

First, suppose that the records are stored in the storing circuit 36 inthe form shown in FIG. 13.

In FIG. 12, the entry address “DataStart” of the first record with theranking 1, which is stored in the storing circuit 36, is assigned to avariable “X”, in step S1. Additionally, the entry address of the nextrecord with the ranking 2 among the records shown in FIG. 13 is assignedto a variable “Y”. In step S2, it is determined whether or not thevariable “X” is larger than a variable “DataEnd”, that is, whether ornot the process is performed for the records in all the entries. If thedetermination results in “YES” in step S2, it means that the process iscompleted for the records in all the entries. Therefore, the process isterminated. If the determination results in “NO” in step S2, a record tobe processed is left. Therefore, the flow goes to step S4, where it isdetermined whether or not the variable “Y” is larger than the variable“DataEnd”. This is intended to determine that the variable “Y”indicating the entry address of the record to be compared with therecord having the entry address equal to the variable “X” exceeds“DataEnd”, that is, no record to be compared is left in the storingcircuit 36. If the determination in step S4 results in “YES”, a recordto be compared reaches the last entry. Therefore, the variable “X”indicating the entry address of the record at the comparison source isincremented by 4, and the value of the variable “Y” is set to a valuewhich is larger than the updated value of the variable “X” by 4 (stepS3). Control then transfers to the next entry record, that is, theprocess of the timing set in the record. If the determination results in“NO” in step S4, the contents of the addresses (X+2) and (Y+2) arerespectively loaded into registers A and B. Each of the addresses “X”and “Y” indicates the address at which the data item of the ranking ofeach record is stored. The address of each entry, to which “2” is added,indicates the address at which the data item of the timing of eachrecord is stored. Accordingly, timing data of each record to be comparedis loaded into the registers A and B. In step S6, the value obtained by(register A-register B) is stored in a register C. Then, it isdetermined whether or not the content of the register C is “0” in stepS7. That is, it is determined whether or not the timing data of the tworecords are the same. This determination is based on the followingconsideration. If signals are transmitted from the same base station,their timing are estimated to be the same even if their frequencies aredifferent. That is, the data at the same timing are those transmittedfrom the base station. Therefore, it is sufficient to leave any one ofthe data.

If the determination results in “NO” in step S7, the signals are not theones transmitted from the same base station. The flow therefore goes tostep S14 where the entry address of the record to be compared is changedto the next entry address. The flow then goes back to step S4, and theabove described process is repeated. If the determination results in“YES” in step S7, it means that the timing data of the two records arethe same. Accordingly, it is judged that the signals are transmittedfrom the same base station, and either of them may be left. The flowthen goes to step S8 where the contents at the addresses “X+3” and “Y+3”are respectively loaded into the registers A and B. In step S9, thevalue obtained by (register B-register A) is stored in the register C.In step S10, it is determined whether or not the register C is largerthan “0”. This is intended to determine which of the correlationalsquare amplitude calculation values of the records at the two entryaddresses “X” and “Y” is larger. Namely, this is based on theconsideration such that it is sufficient to store the signal of a largercorrelational square amplitude calculation value.

If the determination results in “NO” in step S10, the correlationalsquare amplitude calculation value of the record at the entry address“X” at the comparison source is larger. Therefore, the record at thecomparison destination “Y” is changed. Namely, the flow goes to step S14where the value of the variable “Y” is incremented by 4 in order to readthe record in the succeeding entry from the storing circuit 36 bysetting Y=Y+4. The flow goes back to step S4, and the above describedprocess is repeated. If the content of the register C is larger than “0”in step S10, the correlational square amplitude calculation value of therecord to be compared with “X” is larger. Therefore, the records storedat the addresses “X” through “X+3” are rewritten to be those at theaddresses “Y” through “Y+3”. As a result, the records originally storedat the addresses “X” through “X+3” are overwritten and erased. Next, therecords at the address Y+4 and the subsequent addresses are moved aheadto the address Y and the subsequent addresses. Namely, since the recordspreviously stored at the addresses “X” through “X+3” are erased, thestorage locations of the records at the address “Y” and the subsequentaddresses are moved ahead by 1 entry. AT the same time, the records atthe address “Y” and the subsequent addresses “Y+3” are overwritten toprevent the identical data from existing duplicately. In step S13, “4”is subtracted from the variable “DataEnd” indicating the last entryaddress of the latest storage records. After the process in step S14 isperformed, the flow goes back to step S4 and the above described processis repeated. The process in step S13 is intended to move ahead also theentry address of the last record in correspondence with the process foroverwriting and erasing the records at the addresses “X” through “X+3”,and the process for moving ahead the storage locations of the records atthe address “Y” and the subsequent addresses by 1 entry, which isperformed in step S12.

With the above described processes, only the record having the maximumcorrelational square amplitude calculation value is left sequentiallyfrom the timing data having a larger correlational square amplitudecalculation value, and the remaining records are sequentially deleted.Finally, only the record in which the maximum correlational squareamplitude calculation value is set is stored for each timing data in thestoring circuit 36. Additionally, these records are stored in descendingorder of a maximum correlational square amplitude calculation value.

In the example shown in FIG. 13, for the records having the timing “50”,the record at the entry address “DataStart” is left, and the records atthe entry addresses “DataStrt+4” and “DataStart+8” are deleted.Additionally, for the record having the timing “75”, the record storedat the entry address “DataStart+12” is left and the other record isdeleted. Then, the record stored in the entry at the address“DataStart+12” is stored in the entry at the address “DataStart+4”. Therecords having the maximum correlational square amplitude calculationvalue for each timing, which are not shown in this figure, are movedahead also in the respective entries at the address “DataStart+8” andthe subsequent addresses.

The process shown in the above described flowchart is merely oneexample. A plurality of methods for determining whether or not therecord stored in the storing circuit 36 is the record of the signal fromthe same base station, can be considered. For example, an arbitraryentry record may be deleted using a random number without leaving alarger correlational square amplitude calculation value when the recordof the signal from the same base station is deleted.

FIG. 14 is a block diagram showing the configuration of a mobile stationaccording to an eighth preferred embodiment of the present invention.

In this figure, the same constituent elements as those shown in FIG. 11are denoted by the same reference numerals.

This preferred embodiment is a configuration for easily realizing thecapabilities of the seventh preferred embodiment on a mobile stationside. That is, in the seventh preferred embodiment, its process isperformed by estimating the signals transmitted from the same basestation to have the same timing. Actually, however, the signals may havedifferent timing at respective frequencies even if they are transmittedfrom the same base station. This preferred embodiment assumes the casewhere each base station shifts the phases of the common short codes inlong code mask symbol parts of perch channel signals at respectivecarrier frequencies, by a predetermined value common to all of basestations (provides a delay to the frequencies). The long code-maskedsymbol part is the portion 103 which is spread with the common shortcode and the group short code of the perch channel signal 100 in FIG. 1.Since this portion 103 is not spread with a long code, that is, thisportion 103 is in a state where spreading with a long code is maskted,it is referred to as the long code-masked symbol part.

Since the amount of a delay (a delay time?) provided between frequenciesis predetermined in such a system, the amount of a delay to be providedto a received signal frequency can be decided by predetermining whichfrequency is received.

The signal received by an antenna 20 is received by a receiving circuit21. A controlling unit 27 provides frequency specification data to areceiving circuit 21 and converts a particular frequency signal into anIF band signal. The converted IF band signal is input to an orthogonaldemodulator 22, which demodulates the signal into an I and Q signals.After the I and Q signals are respectively converted into digitalsignals by A/D converters 23-1 and 23-2, they are input to matchedfilters 24-1 and 24-2. Then, the correlation values between a commonshort code and the digital I and Q signals are calculated by the matchedfilters 24-1 and 24-2. Then, the correlational power value based on thecorrelation values is calculated by a square amplitude calculatingcircuit 25. Frequency specification data is output from the controllingunit 27 to switches SW1 and SW2, which determine whether or not theoutput from the square amplitude calculating circuit 25 is input to adelay element 40 by using the frequency specified by the frequencyspecification data. Because the amount of a delay provided to respectivecarrier frequencies is predetermined at all base stations, the carrierfrequency signal having a maximum delay is input to a CPU 35 withoutbeing passed through the delay element 40. The correlational powervalues of other carrier frequency signals are input to the delay element40 by turning on/off the switches SW1 and SW2, so that their delayamounts are cancelled. The frequency specification data output from thecontrolling circuit 27 is also input to the delay element 40. The delayelement 40 determines how much the currently selected carrier frequencysignal is delayed from the carrier frequency signal having the maximumdelay, and changes the timing at which the correlational power valueoutput from the square amplitude calculating circuit 25 is input to theCPU 35 based on this determination in order to adjust the amount of adelay from the signal having the maximum delay to be “0”. Additionally,the frequency specification data is input to the CPU 35, and the recordslike those shown in FIG. 13 are stored in a storing circuit 35 in asimilar manner as in the above described preferred embodiment.

As described above, all of the timing at which the correlation powervalues of respective carrier frequency signals transmitted from the samebase station are input to the CPU 35 become identical even if thecarrier frequencies are different. This is because the delay amounts ofthe respective carrier frequencies are cancelled. Accordingly, the dataprocessing based on the estimation such that the input timing of thecorrelational power values of the signals transmitted from the same basestation become identical, can be used when the data stored in thestoring circuit 36 is processed, as referred to in the explanation aboutthe seventh preferred embodiment. Namely, with the configurationaccording to this preferred embodiment, the process of the flowchartshown in FIG. 11 can be applied unchanged even if the signalstransmitted from one base station have different timing at respectivecarrier frequencies.

The CPU 35 then passes a frequency and timing candidates of a perchchannel signal to the controlling unit 27, and makes the controllingunit 27 perform a cell search.

In this preferred embodiment, the delay amounts of frequencies arecorrected by using the switches SW1 and SW2 and the delay element 40.However, the delay correction is not limited to this configuration. Datadelay amounts may be corrected by the software processing of the CPU 35after correlational power values are once stored in the storing circuit36.

By the way, the delay amounts (offset chip amounts include “0”, that is,no delay (offset).

A preferred embodiment to be explained below is intended to prevent anew user from subscribing to a frequency at which traffic is heavy andto promote a new user to subscribe to a frequency at which traffic islight by combining the mobile station/cellular system according to thepreferred embodiments explained so far, and a base station having acapability for obtaining the congested state of the traffic within acell, and by changing the transmission powers of the frequencies atwhich their traffic are heavy and light. Additionally, since a usercapacity is determined by an interference power between channels in aCDMA cellular system, this preferred embodiment can be used to suppressa new subscription when the interference power within a cell becomesequal to or higher than a predetermined level. If a single frequencycell suppresses a newly subscribing user when many frequency cells arecontrolled by one base station, the new user naturally subscribes to anyof the other frequency cells which does not suppress new users.

FIG. 15 is a block diagram showing the configuration of a base stationaccording to a first preferred embodiment of the present invention.

This figures shows the configuration of a transmitting station. As shownin this figure, transmitting units 50-1, 50-2, . . . , whichrespectively generate a signal at a different frequency, are arranged inparallel. Signals output from the transmitting units 50-1, 50-2, . . .are coupled prior to a power amplifier 46, and the coupled signal isamplified by the power amplifier 46. The amplified signal is thentransmitted from an antenna 45.

Because all of the fundamental configurations of the transmitting units50-1, 50-2, . . . are identical except for a difference in thefrequencies of output signals, only the internal configuration of thetransmitting unit 50-1 is shown. Each of the transmitting units 50-1,50-2, . . . obtains the number of users accommodated in its frequencyfrom a managing device in a CDMA cellular system, which is not shown,and inputs the obtained number to a controller 49. Additionally, alsothe data to be transmitted from a base station is input to each of thetransmitting units 50-1, 50-2, . . . , and is modulated by a modulator48. The modulated data is input to a digital control type attenuator 47(not limited to a digital control type). The attenuation amount of thedigital control type attenuator 47 is controlled by an attenuationamount control signal that the controller 49 generates based on thenumber of users in a corresponding frequency. By increasing theattenuation amount of the frequency in which many users are accommodatedand decreasing the attenuation amount of the frequency in which fewusers are accommodated within the transmitting units 50-1, 50-2, . . . ,the signal having the frequency in which few users are accommodated istransmitted with great strength. In this way, when a mobile stationcomprising a receiving device according to any of the first through theeighth preferred embodiments is used, many new users are accommodated ina frequency where few users are accommodated when using a mobile stationcomprising a receiving device according to any of the first through theeighth preferred embodiments. Assume that the transmission power of aperch channel at a frequency whose traffic is heavy is “P1”, and thetransmission power of the perch channel at the frequency whose trafficis light is “Pg”. If P1>Pg is satisfied at this time, the probabilitythat most new users within a service area subscribe to the frequencywhose traffic is light becomes high. If “P1” is set to be sufficientlylarge for “Pg”, it becomes possible to accommodate most of the new usersin a cell whose traffic is light.

This implementation is for the case where the transmission power of aperch channel at a single carrier frequency is controlled. A modulationoperation such as spreading, etc. is performed for the data transmittedon the perch channel, and its transmission power is adjusted by thecontroller 49 with the attenuator 47 which can control the attenuationamount. Then, the data signal is amplified by the power amplifier 46 andis transmitted. The number of transmission users within the cell isinput to the controller 49 as data, and the attenuation amount of theattenuator 47 is determined with this data.

Additionally, if the level of a common short code in a perch channelsignal in a certain carrier frequency cell is sufficiently lowered andif the remaining portion of the perch channel signal except for thecommon short code portion is transmitted and left unchanged, no moreusers can newly subscribe to the cell. If the base station sets thepower of the common code spread signal in a perch channel signal of adifferent carrier frequency for the cell to a power higher than thepower of the certain carrier frequency spread signal at this time, mostnew users subscribe to the cell having the carrier frequency at whichthe transmission power of the common short code is higher. Consideringnoise, interference, etc., 100 percent new users do not always subscribeto the cell having the carrier frequency at which the transmission powerof the common short code spread signal is higher. However, this tendencygrows as the difference between the transmission powers increases. If amobile station requires a common short code spread signal at the time ofhandover to a certain cell, it becomes possible to disable the handoverto the cell. It doesn't matter if a user currently existing in the cellrequires the broadcast information (spread by a signal other than thecommon short code) about a perch channel signal during a call in thiscase, because this information is continuously broadcast.

Furthermore, the above described implementations are available also to abase station which physically separates and accommodates cells havingdifferent carrier frequencies. For example, many mobile stationstemporarily concentrate in a particular area in some cases when an eventsuch as a festival is held. In such a case, problems such as adifficulty in making a telephone call, a degradation in a speechquality, etc. can possibly occur because the accommodation capacity ofan existing base station is exceeded. When the number of users reaches apredetermined number at an existing base station in this case, the powerof the common short code spread signal is minimized (reduced to “0” ifpossible) and the power of the short code spread signal at a basestation arranged on demand is transmitted at a normal level, thereafter,most users come to subscribe to the cell at the base station arranged ondemand. As a result, the problems such as a difficulty in making atelephone call and a degradation in a speech quality can be preventedfrom occurring. There is an advantage to a mobile station that theinitial cell search time does not increase. Additionally, this method isavailable for the system where a perch channel exists in a singlefrequency although the system itself uses a plurality of carrierfrequencies. In this case, a mobile station makes an initial cell searchfor the single frequency.

FIG. 16 is a block diagram showing the configuration of a base stationaccording to a second preferred embodiment.

This figure assumes only “f1” and “f2” to be the frequencies used by thebase station. However, the number of frequencies used by the basestation is not always limited to two.

This preferred embodiment is intended to independently control only thetransmission power of a common short code spread signal on a perchchannel. Remaining data except for the long code-masked portion on theperch channel is orthogonally multiplexed by orthogonal modulators 56-1and 56-2, and the multiplexed data is spread with a common short code byshort code spreading units 58-1 and 58-2. The common short code isspread (despread) with a long code by long code despreading units 57-1and 57-2, weighted (amplified with gains “g1” and “g2”) by amplifiersAMP1 and AMP2, and time-multiplexed with the data output from the shortcode spreading units 58-1 and 58-2. Here, adders 59-1 and 59-2 performan exclusive-OR operation. The time-multiplexed signal is spread withthe long code by long code spreading units 60-1 and 60-2. A transmittingunit 55-1 frequency-converts the signal spread with the long code into asignal having a frequency “f1”, and outputs the signal. In the meantime,a transmitting unit 55-2 frequency-converts the signal spread with thelong code into a signal having a frequency “f2”, and outputs the signal.The signals having the frequencies “f1” and “f2” are coupled by acoupling unit 54, and power-amplified by a power amplifier 53. Then, theamplified signal is transmitted from an antenna 52.

The reason that the common short code is spread with the long code bythe long code spreading units 60-1 and 60-2 after being despread withthe long code by the long code despreading units 57-1 and 57-2 is toprevent the long code-masked portion from being spread with the longcode. Namely, the common short code is spread with the long code afterbeing despread with the same long code, so that the long code iscancelled and the common short code itself is output.

The gains “g1” and “g2” of the weighting of the amplifiers AMP1 and AMP2are determined according to the number of users within a cell in thecontrolling unit 62. The number of users within a cell is obtained fromthe notification from an intra-cell user number counting unit 63arranged as a user monitoring capability of a CDMA cellular system. Thatis, the gains “g1” and “g2” of the amplifiers AMP1 and AMP2 within thetransmitting units 55-1 and 55-2 having a frequency in which a largenumber of users within a cell is accommodated are decreased, while thegains “g1” and “g2” of the amplifiers AMP1 and AMP2 within thetransmitting units 55-1 and 55-2 having a frequency in which a smallnumber of users within a cell is accommodated are increased. Iforthogonal modulation is not performed, the orthogonal modulators 56-1and 56-2 shown in FIG. 15 are unnecessary. Additionally, if a perchchannel is arranged in a single carrier wave frequency depending on asystem, only one transmitting unit is sufficient to implement thispreferred embodiment.

Or, not the number of users, but a signal-to-interference power ratio, asignal-to-(interference+noise power) ratio, an interference power, or aninterference+noise power can be used. These items of information can bemeasured with a known technique. These information are input to thecontrolling unit 62 instead of the number of users in such a case. Thatis, the number of users that can be accommodated within a cell dependson the level of an interference power or a noise power. Therefore, thegains “g1” and “g2” can be adjusted to allow the maximum number of usersto be accommodated in a cell without exceeding the number of users thatcan be accommodated within the cell.

A transmission-to-interference power ratio base station side measuringunit or an interference power measuring unit, which is intended forcontrolling a transmission power of a CDMA cellular system, is madecommon to that used in this preferred embodiment, thereby reducinghardware amount, an operation amount, and a consumption power.

FIG. 17 is a block diagram showing the configuration of a base stationaccording to a third preferred embodiment of the present invention.

In this figure, the same constituent elements as those shown in FIG. 16are denoted by the same reference numerals.

This preferred embodiment is intended to control the transmission powerof a perch channel signal in each carrier frequency at a base stationaccording to the number of users within a visited cell, or to controlthe base station transmission power of the signal spread with the commonshort code within a perch channel signal in each carrier frequency. Inthis case, the above described transmission power is controlledaccording to an average traffic volume including potential traffic.Namely, the base station according to the second preferred embodimentdetermines the gains “g1” and “g2” of the amplifiers AMP1 and AMP2 basedon the number of users that actually access the base station. However,according to the third preferred embodiment, a base station determinesthe gains “g1” and “g2” of amplifiers AMP1 and AMP2 based on the numberof users existing within a cell that the base station itself covers. Forexample, a controlling unit 62 can learn the number of users to beaccommodated by the local base station from the number of users within avisited cell. Therefore, the gains “g1” and “g2” of the amplifiers AMP1and AMP2 are controlled to allocate the frequency channels possessed bythe local base station to the users as efficiently as possible. Forexample, if the users are evenly accommodated in all of the frequenciespossessed by the local base station, the amplifiers AMP1 and AMP2 areswitched to increase the gains at predetermined time intervals. As aresult, the channels used by the visiting users can be allocated almostevenly.

With the configuration according to this preferred embodiment, after thenumber of users within a visited cell is obtained, it is compared withthe number of users within a visited cell of a different station. Ifmany mobile stations exist in a cell of a next base station and if fewmobile stations exist in a cell of a local base station, the gains “g1”and “g2” of the amplifiers AMP1 and AMP2 are increased to accommodatethe mobile stations existing in the cell of the next base station in thelocal base station. In this way, the situation where many mobilestations access a particular base station, which cannot accommodate allof the mobile stations, can be prevented.

Since the number of users within a visited cell is normally stored in aCDMA cellular system visit location register outside a base station, thenumber is read from this register. Unlike a normal visit locationregister, the visit location register according to this preferredembodiment also grasps in which base station area each mobile stationstays.

The transmission data in the portions except for the long code-maskedportions are orthogonally modulated by orthogonal modulators 56-1 and56-2, and spread with a common short code by short code spreading units58-1 and 58-2. Then, these portions are spread by long code spreadingunits 60-1 and 60-2, and frequency-converted into signals havingrespective frequencies. The frequency-converted signals are coupled by acoupling unit 54, and the coupled signal is transmitted from an antenna52 via a power amplifier 53. After the portions of the common short codein the long code-masked portions are despread with a long code by longcode despreading units 57-1 and 57-2, they are amplified with the gains“g1” and “g2” by the amplifiers AMP1 and AMP2. The amplified signals aretime-multiplexed with the data from the short code spreading units 58-1and 58-2 by adders 59-1 and 59-2, and are spread by the long codespreading units 60-1 and 60-2. After the spread signals arefrequency-converted into signals having respective frequencies, they arecoupled by the coupling unit 54, and the coupled signal is transmittedfrom the antenna via the power amplifier 53.

FIG. 18 is a block diagram showing the configuration of a base stationaccording to a fourth preferred embodiment of the present invention.

In this figure, the same constituent elements as those shown in FIG. 17are denoted by the same reference numerals.

According to this preferred embodiment, the measurement result of anupward signal-to-interference power ratio, a signal-to-(interferencepower+noise) ratio, an interference power, or an interference+noisepower at a base station is averaged, and the averaged value is used tocontrol the transmission power of a transmitting unit having eachfrequency in a CDMA cellular system.

Especially, in the configuration shown in FIG. 18, the weight of acommon short code is determined by a controlling unit 62 based on theaverage of the measurement value of a wireless linesignal-to-interference power ratio at each frequency at a base station.This wireless line signal-to-interference power ratio is also used tocontrol the upward transmission power of each wireless line. An SIRmeasurement method is already known. Also the configuration formeasuring Eb/IO can be implemented instead of the SIR.

Namely, the signal-to-interference power ratios (SIRs) measured by awireless line 1 SIR measuring unit 66-1 through a wireless line N SIRmeasuring unit 66-N are averaged by an averaging unit 65 for eachfrequency, and the obtained data is provided to a controlling unit 62.The controlling unit 62 performs control so as to decrease theamplification gain of the amplifier for a transmitting unit 55 havingthe frequency whose SIR value is large, and to increase theamplification gain of the frequency whose SIR value is small based onthe averaged SIR data for each frequency input from the averaging unit65. As a result, the frequency whose SIR value is large, that is, thefrequency of a low communication quality accommodates only a few users,while the frequency whose SIR value is small can accommodate many users.As a result, a service of a high communication quality can be providedas a whole.

Since other configurations and operations according to this preferredembodiment are similar to those of the above described base stationsaccording to the second and the third preferred embodiments, theirexplanations are omitted here.

Additionally, the above described mobile station and base stationsaccording to the preferred embodiments of the present invention can alsobe applied to a system having a single carrier frequency. A mobilestation is assumed to select the cell whose common short code receptionlevel is the highest as a visited cell as referred to in theconventional technique. If the transmission power of the common shortcode spread signal on the perch channel at a certain base station is setto a level lower than that of a peripheral base station at a singlecarrier frequency, the mobile station subscribes to the cell of the basestation whose transmission power of the common short code is higher. Asa result, a subscription to a particular base station can be restricted.On the other hand, if the transmission power of the common short codespread signal on the perch channel at a certain station is set to avalue higher than that of a peripheral base station, a subscription tothe perch channel can be promoted. In this case, some users peripheralto the base station whose transmission power is lowered subscribe to thecell of a base station peripheral to that base station. Because therespective preferred embodiments according to the present invention areapplied to a system having a single carrier frequency by using only asingle carrier frequency in the configurations of the respectivepreferred embodiments, their detailed explanations are omitted here. Insuch a system, a mobile station may make a cell search at a singlefrequency as indicated by the conventional technique.

The above explanation is simplified and provided in such a way that onlya common short code is the code input to the long code despreading units57-1 and 57-2 in the base stations according to the second to the fourthpreferred embodiments of the present invention. Actually, however, acommon short code and a group short code are combined and input.According to the present invention, a mobile station can access the mostsuitable channel of a base station, and at the same time, the basestation can control the channel that the mobile station accessesaccording to the allocation status of mobile stations in a spreadcommunication system, whereby an efficient communication service can beprovided while maintaining a communication quality.

1-20. (canceled)
 21. A mobile communication device that is operationaland performs a cell search of one carrier frequency as result ofadopting a three-stage cell search process in a DS-CDMA system includinga plurality of base stations respectively employing different carrierfrequencies, the mobile communication device comprising: a first searchmeans for performing a first-stage search being a first stage of thethree-stage cell search of a plurality of carrier frequencies; a secondsearch means for performing a second-stage search being a second stageof the three-stage cell search and representing a search of a specifiedcarrier frequency; a third search means for performing a third-stagesearch being a third stage of the three-stage cell search andrepresenting a search of said specified carrier frequency; and acontroller means for selecting a highest strength or highest correlationvalue carrier frequency among the plurality of carrier frequencies basedon a result of the first-stage search to set the selected carrierfrequency as said specified carrier frequency and controlling the secondsearch means and third search means to perform respective searches ofthe specified carrier frequency.
 22. A mobile station that isoperational and performs a cell search of one carrier frequency asresult of adopting a three-stage cell search process in a DS-CDMA systemincluding a plurality of base stations respectively employing differentcarrier frequencies, the mobile station comprising: a first search unitperforming a first-stage search being a first stage of the three-stagecell search and representing a search of a plurality of carrierfrequencies; a second search unit performing a second-stage search beinga second stage of the three-stage cell search and representing a searchof a specified carrier frequency; a third search unit performing athird-stage search being a third stage of the three-stage cell searchand representing a search of said specified carrier frequency; and acontroller selecting a highest strength or highest correlation valuecarrier frequency among the plurality of carrier frequencies based on aresult of the first-stage search to set the selected carrier frequencyas said specified carrier frequency and controlling the second searchunit and third search unit to perform respective searches of thespecified carrier frequency.
 23. A search circuit that is installed intoa mobile station, operational and performs a cell search of one carrierfrequency as a result of adopting a three-stage cell search process in aDS-CDMA system including a plurality of base stations respectivelyemploying different carrier frequencies, the search circuit comprising:a first search unit performing a first-stage search being a first stageof the three-stage cell search and representing a search of a pluralityof carrier frequencies; a second search unit performing a second-stagesearch being a second stage of the three-stage cell search andrepresenting a search of a specified carrier frequency; a third searchunit performing a third-stage search being a third stage of thethree-stage cell search and representing a search of said specifiedcarrier frequency; and a controller selecting a highest strength orhighest correlation value carrier frequency among the plurality ofcarrier frequencies based on a result of the first-stage search to setthe selected frequency as said specified carrier frequency andcontrolling the second search unit and third search unit to performrespective searches of the specified carrier frequency.
 24. A mobilestation that is operational and performs a cell search of one carrierfrequency as result of adopting a three-stage cell search process in aCDMA system including a plurality of base stations respectivelyemploying different carrier frequencies, the mobile station comprising:a first search unit for performing a first-stage search being a firststage of the three-stage cell search and representing a search of aplurality of carrier frequencies; a second search unit for performing asecond-stage search being a second stage of the three-stage cell searchand representing a search of a specified carrier frequency; a thirdsearch unit for performing a third-stage search being a third stage ofthe three-stage cell search and representing a search of said specifiedcarrier frequency; and a controller for selecting a highest strength orhighest correlation value carrier frequency among the plurality ofcarrier frequencies based on a result of the first-stage search to setthe selected carrier frequency as said specified carrier frequency andcontrolling the second search unit and third search unit to performrespective searches of the specified carrier frequency.
 25. A mobilestation that is operational and performs a cell search of one carrierfrequency as result of adopting a three-stage cell search process in aCDMA system including a plurality of base stations respectivelyemploying different carrier frequencies, the mobile station comprising:a first search unit performing a first-stage search being a first stageof the three-stage cell search and representing a search of a pluralityof carrier frequencies; a second search unit performing a second-stagesearch being a second stage of the three-stage cell search andrepresenting a search of a specified carrier frequency; a third searchunit performing a third-stage search being a third stage of thethree-stage cell search and representing a search of said specifiedcarrier frequency; and a controller selecting a carrier frequency amongthe plurality of carrier frequencies based on a result of thefirst-stage search to set the selected frequency as said specifiedcarrier frequency and controlling the second search unit and thirdsearch unit to perform respective searches of the specified carrierfrequency.
 26. A search circuit in a CDMA system which has a pluralityof base stations respectively employing different carrier frequencies,the search circuit selects one carrier frequency among the differentcarrier frequencies to perform a cell search of the one carrierfrequency, the search circuit comprising: a first search unit searchinga plurality of carrier frequencies of the CDMA system; and a controllerselecting a highest strength or highest correlation value carrierfrequency among the plurality of carrier frequencies based on a resultof the first search unit, setting the selected carrier frequency as theone carrier frequency among the different carrier frequencies to performthe cell search of the one carrier frequency.